Sensor to sensor short detection

ABSTRACT

Disclosed is a short detection system for an aircraft. The system includes a pair of alternating current sources defined by respective frequencies being offset by a predetermined value. The system includes a pair of sensor systems including respective measurement circuits coupled to respective sensor apparatuses to measure at least one parameter of an environment. The system includes an alternating current measurement system that includes a low pass filter having a cutoff frequency greater than the predetermined value such that a beat indicative of a difference between the respective frequencies passed through the pair of sensor systems is isolated by the low pass filter. The system indicates a short among the pair of sensor systems when the beat is present.

BACKGROUND

Exemplary embodiments pertain to the art of short detection for sensorsof aircraft. Sensors are prone to measurement failure or measurementaccuracy reduction. One such measurement condition may include a shortbetween two sensors having proximate measurement circuits or loops.Short conditions may not always be conspicuous. For example, thesecommon mode failures may provide similar operator indications amongcommon indication channels that elude detection.

BRIEF DESCRIPTION

Disclosed is a short detection system for an aircraft. The systemincludes a pair of alternating current sources defined by respectivefrequencies being offset by a predetermined value. The system includes apair of sensor systems including respective measurement circuits coupledto respective sensor apparatuses to measure at least one parameter of anenvironment. The system includes an alternating current measurementsystem that includes a low pass filter having a cutoff frequency greaterthan the predetermined value such that a beat indicative of a differencebetween the respective frequencies passed through the pair of sensorsystems is isolated by the low pass filter. The system indicates a shortamong the pair of sensor systems when the beat is present.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the alternatingcurrent sources are reduced by a capacitor before passing through thesensor system.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the sensor apparatusesare thermocouples.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the predeterminedvalue is an order of magnitude less than a frequency of a one of thepair of alternating current sources.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the alternatingcurrent measurement system further includes a rectifier circuit disposedto rectify the alternating current.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the indication isissued when a maximum magnitude of the rectified alternating current isgreater than the predetermined value.

Also disclosed is short detection system for an aircraft. The systemincludes a pair of alternating current sources having respectivefrequencies being offset by a predetermined value. The system includes apair of sensor systems including respective measurement circuits coupledto respective sensor apparatuses to measure at least one parameter of anenvironment. The system includes an alternating current measurementsystem that includes a frequency isolation system that isolates thepredetermined value from an interference alternating currentcorresponding to the pair of alternating current sources having passedthrough the pair of sensor systems. The system indicates a short amongthe pair of sensor systems when the predetermined value is detected.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the frequencyisolation system includes a low pass filter.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the alternatingcurrent sources are reduced by a capacitor before passing through thesensor system.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the sensor apparatusesare thermocouples.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the predeterminedvalue is an order of magnitude less than a frequency of a one of thepair of alternating current sources.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the alternatingcurrent measurement system further includes a rectifier circuit disposedto rectify the alternating current.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the indication isissued when a maximum magnitude of the rectified alternating current isgreater than a predetermined magnitude.

Also disclosed is a method of detecting a short in an aircraft sensorsystem. The method includes driving alternating currents havingrespective frequencies being offset by a predetermined value throughsensor systems including respective sensor apparatuses to measure atleast one parameter of an environment and a measurement circuit coupledto the sensor apparatuses. The method includes detecting presence of aninterference signal comprising a combination of the alternating currentsincluding a beat waveform defined by the offset of respectivefrequencies. The method includes indicating a short among sensor systemswhen the beat is present. The method includes operating an aircraftaccording to the indication.

In addition to one or more of the features described above, or as analternative, further embodiments may include reducing the alternatingcurrent by a capacitor before entering the sensor system.

In addition to one or more of the features described above, or as analternative, further embodiments may include rectifying the interferencesignal and smoothing the rectified interference signal.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the indication isbased on the rectified and smoothed interference signal exceeding apredetermined threshold based on the predetermined value.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 is an aircraft sensor fault detection system having analternating current source; and

FIG. 2A is a Bode plot of frequency response for a low pass frequencyfilter;

FIG. 2B is a Bode plot of frequency response for a high pass frequencyfilter;

FIG. 3 is a multiwave form graph including alternating waveforms,interference alternating waveforms, and a beat waveform; and

FIG. 4 is an algorithm for detecting a short based on an interferencesignal.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the Figures.

Sensor apparatuses may be used to determine various environmentalparameters. For example, thermocouples and resistance temperaturedevices (RTD) may be used to measure a temperature of the environment.Differential pressure devices may be used to measure pressure, fluidflow, or fluid levels. Linear variable differential transformers may beused to measure position.

Sensor apparatuses are associated with sensor or instrument channelsconfigured to provide parameter indication to operators and controlsystems. Channels may be redundantly disposed such that numerousinstruments measure similar parameters and provide indications withinthe same conduits and locations. Common cause faults can occur wheresensor channels short together, providing the same or erroneousindication.

An application of alternating current having unique frequencies throughportions of the measurement circuit and sensor apparatuses maynon-intrusively provide indication of the shorted channels. Indeed, theshort may induce interference waveforms or combination waveforms thatwould flow through one of the channels. The interference waveforms mayhave beat frequencies that, when isolated, provide an indication of theshort. The beat frequencies may further be used to identify combinationsof sensors implicated with a short circuit condition.

Referring to FIG. 1, an aircraft 100, is shown. The aircraft 100includes a sensor systems 101, 151. The sensor system 101 includes asensor apparatus 102. The sensor apparatus 102 may be a thermocouple 104or any other type of sensor, or portion thereof, discussed or notdiscussed throughout this disclosure. As shown, the thermocouple 104 hasdisparate conductors 106, 108 defining a portion of a measurementcircuit 103 connected measurement instrumentation 110, 112 such that avoltage generated by the disparate conductors 106, 108 is measured bythe measurement instrumentation 110, 112. The measurement circuit mayinclude at least the sensor apparatus 102, and the measurementinstrumentation 110, 112. The disparate conductors 106, 108 generate avoltage based on a temperature of the environment of the aircraft 100.The environment may be any enclosed or open area having parameters thatcan be sensed. The parameter may be any property that can be determinedbased on the sensor apparatus 102. As a brief example, the parameter maybe temperature, pressure, mass, weight, position, or velocity.

A source of alternating current 120 may be connected to the sensorsystem 101. The source of alternating current 120 may be configured toflow through the sensor apparatus 102 and the rest of measurementcircuit 103, or a portion thereof. For example, the alternating currentmay be connected in parallel such that alternating current flows throughthe sensor to the alternating current measurement system. Thealternating current 120 may be reduced by a capacitor 122 such that atrickle alternating current is formed. The trickle alternating currentmay impose less measurement error than the full alternating current 120.To filter the alternating current 120 from the measurement circuit 103,a low-pass filter 110 may be implemented. The low-pass filter 110ensures that only direct current or pseudo direct current reaches themeasurement instrumentation 112. The low pass filter 110 may be, forexample, a choke. That is, only direct current provided by thethermocouple 104 or amplification thereof is measured by the measurementinstrumentation 112.

A similar second sensor system 151 includes a sensor apparatus 152. Thesensor apparatus 152 may be a thermocouple 154 or any other type ofsensor, or portion thereof, discussed or not discussed throughout thisdisclosure. As shown, the thermocouple 154 has disparate conductors 156,158 defining a portion of a measurement circuit 153 connectedmeasurement instrumentation 160, 162 such that a voltage generated bythe disparate conductors 156 is measured by the measurementinstrumentation 160, 162. The measurement circuit may include at leastthe sensor apparatus 152, and the measurement instrumentation 160, 162.The disparate conductors 156, 158 generate a voltage based on atemperature of the environment of the aircraft 100. The environment maybe any enclosed or open area having parameters that can be sensed. Theparameter may be any property that can be determined based on the sensorapparatus 152. As a brief example, the parameter may be temperature,pressure, mass, weight, position, or velocity.

A source of alternating current 170 may be connected to the sensorsystem 151. The source of alternating current 170 may be configured toflow through the sensor apparatus 152 and the rest of measurementcircuit 153, or a portion thereof. For example, the alternating currentmay be connected in parallel such that alternating current flows throughthe sensor to the alternating current measurement system. Thealternating current 170 may be reduced by a capacitor 172 such that atrickle alternating current is formed. The trickle alternating currentmay impose less measurement error than the full alternating current 170.To filter the alternating current 170 from the measurement circuit 153,a low-pass filter 160 may be implemented. The low-pass filter 160ensures that only direct current or pseudo direct current reaches themeasurement instrumentation 162. The low pass filter 110 may be, forexample, a choke. That is, only direct current provided by thethermocouple 104 or amplification thereof is measured by the measurementinstrumentation 162.

A short 140 between the sensor systems 101, 151 may cause aninterference waveform to be generated as a combination of thealternating current from sources 120, 170. Although shown between thesensor apparatuses 102, 152, the short 140 may occur at any locationthat the alternating currents 120, 170 traverse. For example, the short140 may occur along portions of the measurement circuits 103, 153.Because the alternating current sources 120, 170 have disparatefrequencies that are offset or different by a predetermined value, theinterference waveform created by the short 140 may include a beat thatis equal to the predetermined value. That is, the beat frequency of theinterference is equal to the difference between the two originatingwaveforms from alternating current sources 120, 170. The predeterminedvalue (e.g., 10 Hz) is an order of magnitude less than a frequency of aone of the pair of alternating current sources.

An alternating current measurement system 105, 155 may detect the beatfrequency. The beat may be isolated by an envelope detector or anotherimplement. For example, a low-pass filter 114, 164 may be used. Thelow-pass filter may be used in conjunction with a precision rectifier orrectifying diode. Additionally, an envelope demodulator circuit may beused. Any type of circuit design that isolates, identifies, or improvesidentification of the envelope is disclosed herein. An additionalrectifier 116, 166 may be further used to convert the envelope or beatsignal into direct current form for comparison at the comparator 118,168. It should be appreciated that any number of beat frequencies may beisolated from any pair of sensors having circuits traversing the sameconduit. That is, each measurement circuit in addition to themeasurement circuits 103, 153 shown may have offset alternating currentsources such that any short between any of the sources would provide aunique beat frequency to the alternating current measurement system 105,155. As such, the alternating current measurement system 105, 155 oradditional alternating current measurement systems could determine theexact pair of devices that was shorted based on the beat frequency orenvelope frequency as isolated.

After isolation by the isolation device, envelope detector, or low-passfilter 114, the alternating current measurement system may be configuredto rectify and smooth the alternating current by a rectification andsmoothing circuit 116. For example, a full-wave rectifier may beimplemented with a capacitor to convert the alternating current todirect current. Other types of rectifiers may be used (e.g., half-wave)and adjustments to the indication thresholds of the comparator 118 maybe adjusted commensurately. The thresholds may be set based on a maximummagnitude of the rectified and smoothed alternating current 120. Forexample, the threshold may be based on a peak value, root mean squaredvalue, or saddle value if the smoothing does not remove all of theoscillations from the source of alternating current 120.

The comparator 118, 168 may compare the rectified direct current with apredetermined threshold based on the difference in frequencies of thealternating current sources 120, 170. For example, a voltage associatedwith the rectified direct current is compared with a voltage associatedwith the difference through evaluation and testing. If the voltage iswithin the particular band or exceeds a threshold, an error indicatingthe short 140 is indicated. It should be appreciated that any or all ofthe portions described herein may be implemented in a microcontroller orcomputer system such that indication is provided For example, theinterference wave form may be received by a computer, controller, orprocessor, configured to isolate the beat waveform.

Referring to FIGS. 2A-2B, Bode plots 200, 250 showing frequency responsefor respective low pass and high pass frequency filters are shown. Bodeplot 200 includes a contour 202 of allowed frequencies in Hz along thehorizontal axis. The Bode plot 200 shows power reduction of −3 dB at thecorner or cutoff frequency 204 along the vertical axis. The cutofffrequency 204 is the division between the pass frequencies and the stopfrequencies. The cutoff frequency for the low pass frequency filter asshown in Bode plot 200 could be 1 Hz. Bode plot 250 includes a contour252 of allowed frequencies in Hz along the horizontal axis. The Bodeplot 200 shows power reduction of −3 dB at the corner or cutofffrequency 254 along the vertical axis. The cutoff frequency for the highpass frequency filter as shown in Bode plot 250 could similarly be 1 Hz.The pass frequency may also be a band (not shown) as a concavecombination of the high pass and low pass frequency filters.

Referring to FIG. 3, a signal plot 300 is shown. 100.00 kHz waveform 302generated from alternating current source 120 is shown. 100.01 kHzwaveform 304 generated from alternating current source 170 is shown. Itshould be appreciated that the frequency of these waveforms may bechanged and adjusted based on a variety of factors not limited to thesensor apparatus used, environment of installation, and other useconditions.

As discussed, the short 140 caused the interference waveform 306 to begenerated. The interference waveform or signal 306 is a combination ofthe frequencies for waveforms 302, 304. The difference in frequencies ofthe waveforms 302, 304 causes an envelope or beat waveform 308 to becreated having a frequency of the difference between waveforms 302, 304,specifically 10 Hz. The beat waveform 306 is defined by an envelope ofthe outer bounds of the waveform. Indeed, this beat waveform 306 can beisolated by the alternating current measurement systems 105, 155 torecognize the short condition between the sensor systems 101, 151.

After rectification, the beat waveform 306 is smoothed to a directcurrent 310 having a magnitude 312. It should be appreciated that themagnitude 312 may be a maximum magnitude based on minor undulationsdifficult to remove by smoothing. The presence of this direct current isindicative that a beat waveform 306 is received by one of thealternating current measurement systems 105, 155. As such, if thismagnitude exceeds a deadband threshold 314, the comparator 168 may issueindication of the short 140.

Referring to FIG. 4, an algorithm 400 is shown. The algorithm 400 startsin step 402. In step 404 the alternating current sources 120, 170 drivealternating current through portions of the measurement circuit 103,153. The portions may include the sensor apparatus 102, 152. The sensorapparatus 102, 152 and portions of the measurement circuit 103, 153 maybe disposed in an environment of an aircraft to measure a parameter ofthe environment. In step 406, an interference waveform 306 is eitherdetected or not detected. The detection may be provided by low-passfilter, beat detector, envelope detector, resistor-capacitor circuit, orany combination thereof. The detection may also include rectification ofthe envelope or beat waveform 308. A comparator 118, 168 may be used todetermine whether the rectified signal 310 is more than noise. The beatwaveform 306 may be defined by the frequency offset of the alternatingcurrent sources 120, 170.

In step 408, the algorithm may include indicating the short 140 amongthe sensor systems 101, 151 to the aircraft or an operator of theaircraft. For example, the alternating current measurement system 105,155, may output a digital output to signify the presence of the short140. The output may include operating the aircraft 100 according to theshort 140. The operation may be performed by an operator or controlsystem of the aircraft 100. In step 412, the algorithm 400 ends orrepeats. It should be appreciated that any of the aforementioned stepsmay be omitted, repeated, or rearranged as necessary. Some of the stepsmay be performed by a controller or computing system. As such, thecomputing system may be configured with any type of programminglanguage, embedded circuit, integrated circuit, logic system, orcombination thereof.

The term “about” is intended to include the degree of error associatedwith measurement of the particular quantity based upon the equipmentavailable at the time of filing the application.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,element components, and/or groups thereof.

While the present disclosure has been described with reference to anexemplary embodiment or embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe present disclosure. In addition, many modifications may be made toadapt a particular situation or material to the teachings of the presentdisclosure without departing from the essential scope thereof.Therefore, it is intended that the present disclosure not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this present disclosure, but that the present disclosurewill include all embodiments falling within the scope of the claims.

What is claimed is:
 1. A short detection system for an aircraft, thesystem comprising: a pair of alternating current sources defined byrespective frequencies being offset by a predetermined value; a pair ofsensor systems including respective measurement circuits coupled torespective sensor apparatuses to measure at least one parameter of anenvironment; and an alternating current measurement system that:includes a low pass filter having a cutoff frequency greater than thepredetermined value such that a beat indicative of a difference betweenthe respective frequencies passed through the pair of sensor systems isisolated by the low pass filter; and provides an indication of a shortamong the pair of sensor systems when the beat is present.
 2. The shortdetection system of claim 1, wherein the alternating current sources arereduced by a capacitor before passing through the sensor system.
 3. Theshort detection system of claim 1, wherein the sensor apparatuses arethermocouples.
 4. The short detection system of claim 1, wherein thepredetermined value is an order of magnitude less than a frequency of aone of the pair of alternating current sources.
 5. The short detectionsystem of claim 1, wherein the alternating current measurement systemfurther includes a rectifier circuit disposed to rectify an alternatingcurrent.
 6. The short detection system of claim 5, wherein theindication is issued when a maximum magnitude of the rectifiedalternating current is greater than the predetermined value.
 7. A shortdetection system for an aircraft, the system comprising: a pair ofalternating current sources having respective frequencies being offsetby a predetermined value; a pair of sensor systems including respectivemeasurement circuits coupled to respective sensor apparatuses to measureat least one parameter of an environment; and an alternating currentmeasurement system that includes a frequency isolation system thatisolates the predetermined value from an interference alternatingcurrent corresponding to the pair of alternating current sources havingpassed through the pair of sensor systems, and provides an indication ofa short among the pair of sensor systems when the predetermined value isdetected.
 8. The system of claim 7, wherein the frequency isolationsystem includes a low pass filter.
 9. The short detection system ofclaim 7, wherein the alternating current sources are reduced by acapacitor before passing through the sensor system.
 10. The shortdetection system of claim 7, wherein the sensor apparatuses arethermocouples.
 11. The short detection system of claim 7, wherein thepredetermined value is an order of magnitude less than a frequency of aone of the pair of alternating current sources.
 12. The short detectionsystem of claim 7, wherein the alternating current measurement systemfurther includes a rectifier circuit disposed to rectify an alternatingcurrent.
 13. The short detection system of claim 12, wherein theindication is issued when a maximum magnitude of the rectifiedalternating current is greater than a predetermined magnitude.
 14. Amethod of detecting a short in an aircraft, the method comprising:driving alternating currents having respective frequencies being offsetby a predetermined value through sensor systems including respectivesensor apparatuses to measure at least one parameter of an environmentand a measurement circuit coupled to the sensor apparatuses; detectingpresence of an interference signal comprising a combination of thealternating currents including a beat waveform defined by the offset ofrespective frequencies; indicating a short among the sensor systems whenthe beat is present; and operating an aircraft according to theindication.
 15. The method of claim 14 further comprising, reducing thealternating current by a capacitor before entering the sensor system.16. The method of claim 14 further comprising, rectifying theinterference signal and smoothing the rectified interference signal. 17.The method of claim 16, wherein the indication is based on the rectifiedand smoothed interference signal exceeding a predetermined thresholdbased on the predetermined value.